1. Field of the Invention
This invention relates to a process for preserving blood platelets for clinical use and to a frozen concentrate containing blood platelets. More especially, this invention is directed to a process for freezing blood platelets by contacting them with an aqueous saline solution containing glycerol and glucose and freezing the same rapidly, following removal of supernatant liquid, at a rate of at least 20.degree. C per minute. This invention is particularly concerned with the intact proteinaceous mass resulting from the thawing of the concentrated blood platelets which mass can be used directly without glycerol removal for infusion into a recipient for the purpose of effecting hemostasis.
2. Discussion of the Prior Art
The growing need for human platelets in clinical medicine and the relatively short period during which they can be stored emphasized the potential usefulness of a method for their cryopreservation. These platets are in such increased demand and the increase is steadily upwards. For instance, one major metropolitan blood center has increased the number of units prepared from 56,370 in 1970 to 105,200 in 1974.
Platelets are known to be extremely sensitive to processing and can readily be rendered inactive during a freezing technique. A number of investigators have looked to the use of dimethyl sulfoxide (DMSO) as a cryopreservative agent for the platelets. The general procedure has been to apply a solution of dimethyl sulfoxide to the platelets to preserve the same during a slow freezing operation. When the platelets are to be used the frozen mass is thawed. However the dimethyl sulfoxide must then be removed from the mass.
The toxicity and odor associated with dimethyl sulfoxide preclude its use unless these platelets are washed to remove the DMSO prior to transfusion. Hence, researchers have looked to other materials as cryopreservative agents.
One pair of researchers has looked to the use of glycerol as a cryopreservative agent. It has been proposed to treat the platelets with a 12% glycerol solution and to freeze the same quite slowly at a rate of about 1.degree. C per minute. Thus Cohen and Gardner reported in New England Journal of Medicine 274 1400-1407 (1966) the freezing of platelets in 12% glycerol at a slow rate of cooling. This resulted in a relatively low recovery of platelets and there has been observed difficulties in the removal of glycerol from the platelet mass prior to transfusion. Other researchers (Dayian, G. and Rowe, A. W, Cryobiology 6, 579 (1970) observed that 12% glycerol causes extensive damage to platelet lysosomes and this platelet injury is further aggravated by freezing.
It has therefore become desirable to provide an alternative to the DMSO cryopreservative agent and to provide an acceptable means for the freezing of platelets. It has become desirable particularly to provide a process for the freezing of blood platelets by an agent which does not cause platelet damage either by its application to the platelets or during the subsequent freezing operation. More especially, it has become desirable to provide a process for the freezing of blood platelets by the use of a cryopreservative agent which is compatible with the platelets and does not have to be removed prior to transfusion of the platelet mass into a recipient.